Field of the Invention
The present invention relates to a resist composition, a method for forming a resist pattern, a compound, and an acid generator.
This application claims priority to Japanese Patent Application No. 2016-128162, filed Jun. 28, 2016, the entire content of which is hereby incorporated by reference.
Background Art
A lithography technique includes steps of forming a resist film composed of a resist material on a substrate, selectively exposing the resist film and performing a developing treatment, thereby forming a resist pattern having a predetermined shape. A resist material in which an exposed area of the resist film is dissolved in a developing solution is referred to as a positive-type resist material, and a resist material in which an exposed area of the resist film is not dissolved in a developing solution is referred to as a negative-type resist material.
In recent years, in the manufacturing of semiconductor devices and liquid crystal display elements, pattern miniaturization has been rapidly progressed in accordance with the progress of the lithography technique. As a miniaturization technique, generally, shortening the wavelength (realizing high energy) of an exposure light source has been performed. Specifically, ultraviolet rays represented by a g-line and an i-line was used in the related art, but KrF excimer laser or ArF excimer laser has been used for the mass production of semiconductor devices these days. In addition, with such an excimer laser, studies regarding extreme ultraviolet rays (EUV) having a short wavelength (high energy), electron beams (EB), and an X-ray have been conducted.
The resist material is required to have lithography properties such as sensitivity with respect to the exposure light sources and resolution capable of reproducing patterns having a minute dimension.
In the related art, as a resist material satisfying such a requirement, a chemically amplified resist composition containing a base material component whose solubility in the developing solution changes under the action of an acid, and an acid generator component which generates an acid upon exposure has been used.
For example, in the case where the developing solution is an alkali developing solution (alkali developing process), a chemically amplified positive-type resist composition which contains a resin component (a base resin) whose solubility in the alkali developing solution increases under the action of the acid and an acid generator component is typically used. When a resist film formed by the aforementioned resist composition is selectively exposed to the light at the time of forming a resist pattern, an acid is generated in the exposed area from the acid generator component, the polarity of the base resin is increased under the action of the acid, and thereby the exposed area of the resist film becomes soluble in the alkali developing solution. For this reason, a positive-type pattern in which an unexposed area of the resist film remains as a pattern is formed by alkali developing.
On the other hand, in the case where such a chemically amplified resist composition is applied to a solvent developing process in which a developing solution (an organic developing solution) containing an organic solvent is used, the solubility in the organic developing solution is relatively decreased when the polarity of the base resin is increased, and thus the unexposed area of the resist film is dissolved and removed by the organic developing solution so as to form a negative-type resist pattern in which the exposed area of the resist film remains as a pattern. The solvent developing process in which such a negative-type resist pattern is formed is referred to as a negative-type developing process in some cases.
The base resin used for the chemically amplified resist composition generally has a plurality of structural units for improving the lithography properties.
For example, in the case of the resin component in which the solubility in the alkali developing solution is increased under the action of the acid, a structural unit including an acid-decomposable group which is decomposed by the action of an acid generated from the acid generator or the like so as to increase the polarity is used, and a structural unit including a lactone-containing cyclic group and a structural unit including a polar group such as a hydroxyl group are also used in combination.
In addition, in the forming of the resist pattern, behavior of the acid generated from the acid generator component upon exposure is regarded as one element that greatly affects lithography properties.
As an acid generator used in the chemically amplified resist composition, various kinds of acid generators have been proposed. For example, an onium salt-based acid generator such as an iodonium salt and a sulfonium salt, an oxime sulfonate-based acid generator, a diazomethane-based acid generator, a nitrobenzylsulfonate-based acid generator, an iminosulfonate-based acid generator, and a disulfone-based acid generator have been known.
As the onium salt-based acid generator, those containing an onium ion such as triphenylsulfonium in a cation part are mainly used. In an anion part of the onium salt-based acid generator, an alkylsulfonic acid ion or a fluorinated alkylsulfonic acid ion in which at least one hydrogen atom of an alkyl group is substituted with a fluorine atom is generally used.
In addition, in order to improve the lithography properties in the forming of the resist pattern, as the anion part of the onium salt-based acid generator, an onium salt-based acid generator which contains an anion having a specific structure containing an aromatic ring also has been proposed (for example, refer to Japanese Patent No. 5149236).